1. Field of Invention
Since the invention of the pneumatic tire by Robert Thompson in 1845, the original art and concepts of tire technology have slowly evolved toward a more scientific understanding of how a tire performs. Certainly it is logical to assume that the original tire as invented probably claimed as one of its attributes the ability to cushion carriages from road shock since the tire itself appears to have been little more than a heavy inner tube covered with a layer of tough, durable leather. The original invention never became popular as evidenced by historical events, and it is again reasonable to assume that a major reason for the tires' failure to achieve popularity may have been associated with the primitive state of rubber chemistry, especially vulcanization, and this primitive state of knowledge probably resulted in an inner tube of extremely poor durability. From the beginning, carriage ride and tire durability have been inextricably intertwined. Since hindsight is possessed with 20/20 vision, it becomes obvious from studying tires' historical past that the concepts of softer ride inherent in the pneumatic tire continued to occupy a dominant position in tire technologists' minds and further that this concept was continuously being tempered by the practical reality of manufacturing tires with adequate durability.
The original pneumatic tires were built on mandrels shaped to duplicate the tire's air cavity and the earliest reinforcement material used was square woven cotton cord fabric. The problems associated with trying to wrap an 80" long piece of fabric around the mandrel and to uniformly compress the fabric to the lesser length dictated by the circumference of the beads of the tire, forced someone to invent the first expandable drum type of tire building machine which permitted the tire to be built on a flat drum so that the green tire as built resembled an open ended barrel configuration which is then lifted or lofted into the toroidal configuration typical of tires built originally on mandrels. At this stage, the mass of steel, rubber, and cord is set by vulcanization. Expandable drum building machines vary in minor detail and the same machine can be used to build a variety of sizes by the simple expedient of making the building drum wider as a larger cross section tire is required.
Tire development takes place slowly and each new development nominally is predicated upon a previous tire's deficiencies in the market place as contrasted to an engineer's starting out with a clean sheet of paper to design an entirely new tire. One such entirely new development and conception of the pneumatic tire was the original radial tire which differed in the extreme from the conventional tires made wherein square woven fabric was used. The original radial tires as built utilized cord, as contrasted to square woven fabrics in use in "bias" constructed tires. The original introduction of cords as we know them today was simply a step of unravelling the warp and woof of square woven fabric existent in one plane to where the warp cords were segregated in one plane separate and distinct from the woof cords segregated in still another plane.
Tires from their very inception by Thompson have unfortunately been prone to undergo destructive failure in contrast to their successfully wearing out. The original aim of tire manufacturing companies was to increase the number of miles a tire would go before it did fail. The next step in the improvement of tire durability was to build tires that might wear out before they failed, and this was followed by the desire to make tires go a greater number of miles before they would wear bald, and about the time that this objective may have been achieved, the further limitation was imposed to make the tire softer riding which resulted in more tire failures, ad infinitum.
Almost everyone attempting to build a better tire traditionally insists upon arranging all cord paths of each individual ply fabric in straight curvilinear lines with the reasoning being that the straighter the cord, the more uniform will be the tension within and between the various cords; and therefore, the more uniform the tire will be so far as regards its dynamic stability. This hypothesis is urged in my issued Pat. No. 3,807,475 as well as in U.S. Pat. No. 3,563,088 and U.S. Pat. No. 3,722,270, and others.
Tire failure has been traditionally associated with lack of tire strength. When a tire fails, tire design engineers by rote increase tire strength either by putting more cords in the tire body, or by making each cord bigger so that each cord is stronger in itself, or by going to a stronger cord of a different chemical composition. Thus, the original cotton cord was replaced by rayon which in turn was partially replaced by nylon which in turn was partially replaced by polyester, and ad infinitum to steel, glass fiber and most recently Fibre B or Kevlar which is also enjoying considerable success in the manufacture of bullet proof modern and stylish dresswear.
A problem with increasing tire strength by increasing numbers of cords within a given number of plies or by increasing the number of plies or by increasing the thickness of plies necessitated by use of larger cords is that the tire's bulk is increased which in turn affects the tire's ability to dissipate heat which in turn adversely affects the tire's durability. So increasing a tire's strength by these cited conventional means is not always the only answer to increasing a tire's durability.
This brings into focus the other major property of a tire--its elasticity. If a tire cannot be made strong enough by continuously beefing up its strength by one or more of the means enumerated, permitting the tire to roll over a surface protrusion without breaking, then possibly the tire can be made to envelop the same protrusion by making the tire more elastic. Rubber in itself is noted for its elasticity, but a rubber's strength and modulus alone are inadequate to contain the air supporting the load without the stiffening reinforcement imparted by tire cord. To improve tire elasticity and fatigue resistance which is broadly synonymous with tire durability, tire cords were given a twist which made them resemble miniature coil springs.
Tire cord consists of a number of very small filaments of cord material where the diameter of the filaments is roughly 001" but varies from material to material. The filament is the smallest component of cord that has the appearance of length. From 25 to 600 of these small filaments are extruded and twisted about the bundle axis to form a yarn. Two or three yarns in turn are twisted together to form the cord. The twist of the yarn or ply is usually about the same magnitude as the final cord twist but is in the opposite direction, the yarn bundles are twisted in the opposite direction which in effect untwists the yarn bundle so that the yarn bundle has little or no twist in the final cord. The direction or twist of tire cords is referred to as being either Z or S twist which means simply that the direction of twist with respect to the axis of the cord is in the same direction as the cross member of the letters Z or S. Thus, in a cord, the yarn might be given a Z twist and the cord an S twist. Tire yarns and cords are given twist to improve the cords fatigue and elastic characteristics when used to reinforce a tire. Generally, an increase in cord fatigue life, brought about by greater twist, is offset by a reduction in cord tensile. The designation 840/140/2 for a tire cord simply means that the yarn has a denier of 840, that there are 140 filaments per yarn bundle, and there are two ply yarns per cord. Ofttimes the second number is omitted from a tire's cords' designation. The designation 12S.times.12Z coupled with a 1260/2 means 12 twists per inch for S turns in the yarn bundle and 12 turns per inch for Z turns of the two yarn bundles in the cord cable made from 1260 denier filaments.
Thus, tire strength and durability as reflected by the tire's elasticity and strength has traditionally been closely allied to cord type as well as mechanical arrangement of individual elements. The two factors of tire strength and elasticity in essence resemble the square woven fabric whose warp and woof were inextricably intertwined until they were separated into their individual components of a warp ply of individual parallel aligned cords and a woof ply of identical cords in a mirror image to the warp ply.
Attempts have been made to combine radial and biased plies into a single tire structure. The attempts universally have been accompanied by various expedients directed towards maintaining straight curvilinear cord paths. However, if it were possible to take all of the desirable attributes of a biased constructed tire while minimizing its bad features, and add them to the desirable features of a radial ply tire, while minimizing the radial ply tires' drawbacks, the resultant hypothetical tire would indeed be an astounding new item of commerce. It would outperform other tires in all sorts of different driving conditions. The tire would be structurally stronger because of the interlaced crisscross cord paths of the various ply constructions. Vehicle performance, tire mileage, and overall operating safety would be improved in such a tire construction.
While it is technically possible it is commercially impractical to produce a tire of mixed biased and radial ply construction wherein the cord paths of both the radial and biased ply cords follow along the axial centerline of the perfectly aligned theoretical cord paths. This is especially so when the fabrication is carried out on conventional bias tire building drums.
Therefore, should it become practical to incorporate a mixed biased and radial ply construction into a tire which could be built on existing bias tire building drums and vulcanized by utilizing available bias tire vulcanizing equipment, such an expedient would be desirable. Such a desirable goal would be especially meritorious if the resulting tire structure offered novel improvements over present known tires or over the anticipated combination of tire properties referred to above.
2. Description of the Prior Art
______________________________________ 1. Ehle 1,364,870 2. Kraft 2,179,374 3. Darrow 2,703,128 4. Beckadolph 2,976,905 5. Kraft 3,108,628 6. Manchetti et al 3,165,138 7. Massoubre 3,231,000 8. Kovac et al 3,217,778 9. Bridge Jr. 3,419,059 10. Mirtain 3,442,315 11. Duduk 3,672,423 12. Curtis Jr. 3,780,783 13. Cooper & Brierly British Patent 730,878 14. Rushen British Patent 251,206 15. Continental British Patent 1,206,528 16. Berringer 3,402,752 17. Zimmerman 3,393,252 18. Trevaskis British Patent 814,248 19. Dunlop French Patent 1,303,287 20. Vittorelli 2,990,870 21. Beckadolph 2,986,191 22. Dunlop French Patent 1,445,693 23. Beckadolph German Patent 1,073,331 24. Mirtain 3,363,660 25. Mirtain 3,242,968 26. Jacobs 3,068,926 ______________________________________
Kraft (U.S. Pat. No. 2,179,374) recognized the need for a tire with increased elasticity which would have the capability of enveloping rather than rolling over a protruding object in a roadway, and his solution was to mechanically orient the otherwise parallel tire cords into a sine curve form by alternately bending them back and forth during or after the calendering operation but before cutting such cords at a bias angle and building them into his tire. All plies of his tire utilized the substantially uniform sine wave cord configuration.
Kovac (U.S. Pat. No. 3,217,778) sought to achieve increased tire elasticity by purposefully bending or deforming the individual fibers or groups of fibers from their original straight or extruded configuration and heat setting them in their crimped deformed configuration. Kovac, as did Kraft, utilized the novel cord deformed configuration in all plies of his tire.
But neither the Kraft nor Kovac tires were commercial successes, and it is only possible to speculate that their lack of success may be or probably was associated with their tires' inability to maintain a given size. The elasticity of these tires no doubt had indeed been considerably enhanced but alone with the enhanced elasticity came excessive tire growth.
Ehle (U.S. Pat. No. 1,364,870) fabricated the first tire of mixed bias-radial construction in 1919 when tires were still being built on mandrels or cores. All of Ehle's plies were carefully arranged so that all cords were at or nearly at equal tension with said cords of both bias and radial plies being fastened to the steel beads on either side of the tire by ingenious use of special fabric wings to bind together longitudinally the edges of the different cord layers.
Darrow (U.S. Pat. No. 2,703,128) built a mixed tire of radial and bias plies in 1950 and states as a main purpose for his tire the increased strength, especially bursting strength, coupled with lower cost due to use of a lesser amount of cord material as main reasons for his tire. Darrow further notes that "the straight across cords would require a drum several inches narrower than bias cords . . . " but proceeded to build his tire at the narrower drum setting required for the radial tire and compensated for the wider drum setting required by the bias plies by cutting each bias ply the appropriate width required for the particular sized tire he was building with an additional 2" to 21/2", and he then proceeded to cut each ply in two and to lap them in the middle on the building drum. During the tire shaping operation the lap of bias plies slipped so that while the original lap before tire shaping was 21/2", after shaping the lap was reduced to 3/4" in the finished tire. Darrows stated reason for ensuring that all cords, both bias and radial, were straight curvilinear was to minimize compressive stresses within any cords in order that tire durability not be adversely affected.
Technical literature on tires contains many references pointing out the very bad effects upon tire durability of putting tire cords in compression.
Cooper and Brierly (British Pat. No. 730,878) similarly built a tire of mixed radial and bias cords in 1953 and went to great pains to build the bias portion of the body separately from the radial portion of the tire body, anchoring each type cord to separate beads then putting the radial tire body cords atop the bias body cords and adding a tread wearing compound thereto, all in order presumably to ensure all cords' being under similar tension and none being under compression.
Kraft (U.S. Pat. No. 3,108,628) in 1959 built a mixed ply type tire similar to Darrow's and sidestepped the problem of different drum widths' being required by the respective bias and radial cords by first applying the radial cords to the building drum, ingeniously fastening the bias plies to the beads while leaving the bias plies themselves to either side of the tire building drum, then partially expanding or shaping the tire by use of a special feature of his building drum, then folding up the bias plies on either side, lapping them in the crown, applying the tread and sidewall rubber, and then completing the shaping of the tire depending upon less slippage at the top splice than did Darrow. Kraft in his mixed ply bias-radial ply tire took pains to avoid the introduction of the sine wave mechanically shaped cords of his previous invention (U.S. Pat. No. 2,179,374) although it might have been logically deduced that the radial ply cords would have been compressed and possibly to have assumed a sine wave form if he had built his tire on an ordinary bias tire building machine instead of the special machine he employed.
Ehle, Darrow, Cooper and Brierly, and Kraft were all concerned with the tires cords' being "straight" because of the commonly held technical belief that any non-straight cords within a tire result in loss of tire durability. Patentee's own U.S. Pat. No. 3,807,475 has devised a means for eliminating curvy wavy cord paths in order to improve tire durability.
Duduk (U.S. Pat. No. 3,672,423) has also prepared a mixed radial-bias ply tire and as had been done by each of the cited inventors above, utilized means to ensure that all cords would be straight curvilinear. Duduk states "it is a further object of this invention to provide a radial ply tire which can be manufactured in accordance with standard U.S. techniques for manufacturing conventional bias ply tires." Duduk, probably knowing that the building drum width would be greater for his mixed radial-bias tire than required for a straight radial tire thereby resulting in a surplus length of the radially oriented cords, utilized two means to ensure an essentially straight radial cord. One means which he used was to employ a tire cord (nylon) specially heat treated and stretched so that the cord would have high thermal shrinkage, and he specifies "the preferred thermal shrinkage at 190.degree. C. of both plies is approximately 17 percent (12 tpi)." Thus when his tire heated up during vulcanization, the cords would shrink thereby assuring essentially straight curvilinear cord paths. To further ensure straight cord paths, he anchored the radially oriented cords to both beads so as not to lose the beneficial effect of the thermal shrinkage. The preferred thermal shrinkage of 17 percent cited corresponds closely to the excess length of the radial cords over that required for a radial tire of the same size.
Manchetti (U.S. Pat. No. 3,165,138) describes a tire of mixed bias-radial construction wherein the radial cords are tied to the beads and which contains one bias ply tied to one bead and located inwardly of the radial plies. The purpose of the bias ply was to prohibit the radial cords from pulling through the liner compound, and the reason for anchoring only one bead was to ensure all the cords' being essentially straight curvilinear.
Mirtain's (U.S. Pat. No. 3,442,315) tire is similar to Manchetti's but his objective was to control resonant frequencies set up by the tire and vehicle system.
French Pat. No. 1,445,693 describes a tire having a radial inner ply and low crown angle outer bias plies with the bias oriented cords stretched so as to avoid undulations.
Travaskis (British Pat. No. 814,248) describes an ingenious tire with an inward radial ply and outward bias plies wherein the outward bias cords are specially wound onto the inflated unvulcanized radial ply. The technique employed ensured all cords being straight curvilinear and in equal tension.
French Pat. No. 1,303,287 describes an extremely highspeed tire capable of withstanding speeds of 350 rm/hr or greater containing a reinforcing cord ply buried in the tread rubber with the cords in one tire embodiment being radially disposed. The cords lie just below the groove bottoms and extend into the tread ribs in an undulating path corresponding to the tread design of ribs and grooves. The purpose of the cord ply was to help hold the tread and tire sidwall to the cord body of the tire to help resist against the high centrifugal forces generated at the extremely high speeds.
Massoubre (U.S. Pat. No. 3,231,000), Mirtain (U.S. Pat. No. 3,242,965), Beckadolph (U.S. Pat. No. 2,986,191), and Vittorelli (U.S. Pat. No. 2,990,870) were all concerned with utilizing cords of different chemical composition or size, including control of cord angles, to give tires of improved properties. Vittorelli arranged his cords so as to have a decreasing cord modulus from the inner to outer plies with all cords being at the same angles. Beckadolph (German Pat. No. 1,073,331) utilized rubber compounds of different modulus to build an improved tire. Mirtain (U.S. Pat. No. 3,363,660) utilized cords of different stretchabilities to build an improved tire.
Zimmerman (U.S. Pat. No. 3,393,252), Bridge (U.S. Pat. No. 3,419,059), and Berringer (U.S. Pat. No. 3,402,752) describe cord technology developments in composition, twist, heat tensilizing, etc. that resulted in better tire performance.
Curtis (U.S. Pat. No. 3,780,783) describes a three ply tire "in which the cords in two of the plies follow a geodetic cord path and the cords in the third ply follow a conventional path. The individual cords in all of the plies are of the same length and each ply has its radially inner ends turned about the respective bead core."
British Pat. No. 1,206,528 describes a radial tire whose radially oriented body cords are tied to the beads, and having a belt of inextensible cords extending around the tire wherein the radial cords located directly beneath "the belt are formed with undulations to render said part of the carcass substantially free of tension. In practice the maximum amplitude of the undulations ranged between one and three times the thickness of the radial carcass cords."
Beckadolph (U.S. Pat. No. 2,976,905), Jacobs (U.S. Pat. No. 3,068,926), and Rushen (British Pat. No. 251,206) describe the state of the art of various tire developments at various times during the past half century.
All of these cited inventors were united in a common bond in the thrust of their individual inventions to create improved pneumatic tires. They were essentially concerned with controlling and maintaining straight curvilinear cord paths and with controlling some intangible within the tire through use of modulus variation and cord extensibility or stretchability since these were the accepted criteria as the means of achieving their common objective of improved tires.